BEIRUT (Reuters) - One of Islamic State's top commanders in Syria has been killed in a U.S.-led coalition air strike, the coalition's spokesman said on Thursday, corroborating an earlier report.

Abu Jandal al-Kuwaiti, a member of Islamic State's war committee, was killed on Monday by the Tabqa Dam, a strategic objective in northern Syria near Raqqa city, the jihadists' main stronghold in the country, the spokesman said.

The Syrian Observatory for Human Rights, which monitors the war, had reported on Tuesday his probable death in combat as the militants sought to stave off an advance towards the dam by the U.S.-backed Syrian Democratic Forces (SDF).

Kuwaiti was involved in Islamic State's retaking of the ancient city of Palmyra earlier this month and then went to Tabqa to help shore up the jihadists' defences against the SDF, the coalition said.

"Abu Jandal was involved in the use of suicide vehicles, IEDs (improvised explosive devices) and chemical weapons against the SDF ... his death will degrade ISIL's ability to defend Raqqa and launch external operations against the West," the statement said.

The SDF alliance includes the Kurdish YPG militia and is supported by U.S.-led coalition air strikes in northern Syria in its fight against Islamic State.